Vitamin C (L-ascorbic acid) is used as an active ingredient for various kinds of cosmetics in view of its nutritive enriching effect, fair skin producing effect and the like. However, vitamin C itself is a very unstable substance. Accordingly, in general, it is formulated in a cosmetic as a vitamin C derivative having improved stability such as L-ascorbic acid fatty acid ester, or it is formulated as a so-called two-pack type cosmetic wherein vitamin C powder and other ingredients are separately packed in different containers and they are mixed just prior to use the cosmetic.
However, the vitamin C derivative does not always have enough stability. Particularly, in an emulsion cosmetic such as a cream or a milky lotion, it tends to relatively quickly lose its vitamin C effect. In case of a two-pack type cosmetic, indeed, the stability of vitamin C is improved, but it is not satisfactory because it requires extra labor and expense for packing vitamin C and such a trouble as mixing the ingredients prior to use.
Under these circumstances, the present inventor has intensively studied to obtain a novel emulsion cosmetic in which vitamin C is stably formulated. As the result, it has been found that an emulsion cosmetic in which vitamin C is very stably formulated is obtained by previously treating vitamin C or a derivative thereof with an oil and then formulating it into the cosmetic.